The present invention relates to the transmission of Call Detail Records in a telecommunications system and more particularly to the transmission of Call Detail Records between mobile telecommunications networks.
In today's mobile telecommunications networks, the operator of a mobile network is able to maintain tight control over the calls made and services used by its subscribers when they are at home, i.e. when they are registered with the operator's own network. For example, if a subscriber exceeds his calling credit limit the operator can notify the subscriber of this situation and/or can prevent the subscriber from making further calls until his outstanding account is settled. Similarly, where a subscriber makes use of a top-up account, e.g. using scratch cards to credit his account, an operator can restrict the subscriber's access when the subscriber's credit drops to zero.
Such charging control is possible because the Mobile Switching Centre (MSC) which acts as the “local exchange” for a subscriber sends Call Detail Records (CDRs) at regular intervals to a charging node of the subscriber's home network. The frequency at which CDRs are sent is predefined for a given exchange (e.g. every 5 minutes) and is applied to all subscribers registered with that exchange. However, this is only possible when the serving MSC is an MSC of the home network. In the event that a mobile subscriber is registered with an MSC of a foreign network (i.e. the subscriber is “roaming”), CDRs generated by the serving MSC are passed to a home network through a clearing house in so-called TAP files (if necessary, multiple CDRs are collated in the foreign network and the collated CDRs are sent to the clearing house in a single TAP file). The clearing house identifies the destination home network for the TAP files, for example, on the basis of the IMSI code of the calling subscriber. It can take at least two days or even more before the CDRs are forwarded on to the home network.
A home network cannot therefore monitor, in real time or near real time, the charges being incurred by one of its subscribers when that subscriber is roaming in a foreign network. Rather, charging information is only sent periodically from the foreign network to the home network (e.g. every few days). There therefore exists a possibility that fraud by a roaming subscriber will go undetected by the subscriber's home network for some time, and that during that time the home network operator will incur considerable losses.